DESCRIPTION

Long ago it was considered safe to have encrypted passwords openly
visible in the password file.
When computers got faster and people
got more security-conscious, this was no longer acceptable.
Julianne Frances Haugh implemented the shadow password suite
that keeps the encrypted passwords in
the shadow password database
(e.g., the local shadow password file
/etc/shadow,
NIS, and LDAP),
readable only by root.

The functions described below resemble those for
the traditional password database
(e.g., see
getpwnam(3)
and
getpwent(3)).

The
getspnam()
function returns a pointer to a structure containing
the broken-out fields of the record in the shadow password database
that matches the username
name.

The
getspent()
function returns a pointer to the next entry in the shadow password
database.
The position in the input stream is initialized by
setspent().
When done reading, the program may call
endspent()
so that resources can be deallocated.

The
fgetspent()
function is similar to
getspent()
but uses the supplied stream instead of the one implicitly opened by
setspent().

The
sgetspent()
function parses the supplied string
s
into a struct
spwd.

The
putspent()
function writes the contents of the supplied struct
spwd*p
as a text line in the shadow password file format to the stream
fp.
String entries with value NULL and numerical entries with value -1
are written as an empty string.

The
lckpwdf()
function is intended to protect against multiple simultaneous accesses
of the shadow password database.
It tries to acquire a lock, and returns 0 on success,
or -1 on failure (lock not obtained within 15 seconds).
The
ulckpwdf()
function releases the lock again.
Note that there is no protection against direct access of the shadow
password file.
Only programs that use
lckpwdf()
will notice the lock.

These were the functions that formed the original shadow API.
They are widely available.

Reentrant versions

Analogous to the reentrant functions for the password database, glibc
also has reentrant functions for the shadow password database.
The
getspnam_r()
function is like
getspnam()
but stores the retrieved shadow password structure in the space pointed to by
spbuf.
This shadow password structure contains pointers to strings, and these strings
are stored in the buffer
buf
of size
buflen.
A pointer to the result (in case of success) or NULL (in case no entry
was found or an error occurred) is stored in
*spbufp.

The functions
getspent_r(),
fgetspent_r(),
and
sgetspent_r()
are similarly analogous to their nonreentrant counterparts.

Some non-glibc systems also have functions with these names,
often with different prototypes.

Structure

struct spwd {
char *sp_namp; /* Login name */
char *sp_pwdp; /* Encrypted password */
long sp_lstchg; /* Date of last change
(measured in days since
1970-01-01 00:00:00 +0000 (UTC)) */
long sp_min; /* Min # of days between changes */
long sp_max; /* Max # of days between changes */
long sp_warn; /* # of days before password expires
to warn user to change it */
long sp_inact; /* # of days after password expires
until account is disabled */
long sp_expire; /* Date when account expires
(measured in days since
1970-01-01 00:00:00 +0000 (UTC)) */
unsigned long sp_flag; /* Reserved */
};

RETURN VALUE

The functions that return a pointer return NULL if no more entries
are available or if an error occurs during processing.
The functions which have int as the return value return 0 for
success and -1 for failure, with
errno
set to indicate the cause of the error.

For the nonreentrant functions, the return value may point to static area,
and may be overwritten by subsequent calls to these functions.

The reentrant functions return zero on success.
In case of error, an error number is returned.

ERRORS

EACCES

The caller does not have permission to access the shadow password file.

ERANGE

Supplied buffer is too small.

FILES

/etc/shadow

local shadow password database file

/etc/.pwd.lock

lock file

The include file
<paths.h>
defines the constant
_PATH_SHADOW
to the pathname of the shadow password file.

CONFORMING TO

The shadow password database and its associated API are
not specified in POSIX.1-2001.
However, many other systems provide a similar API.

SEE ALSO

COLOPHON

This page is part of release 3.74 of the Linux
man-pages
project.
A description of the project,
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and the latest version of this page,
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